Purification and partial characterization of a plasminogen activator inhibitor from the human glioblastoma, U138

Ruta graveolens L. induces death of glioblastoma cells and neural progenitors, but not of neurons, via ERK 1/2 and AKT activation

Glioblastoma multiforme is a highly aggressive brain tumor whose prognosis is very poor. Due to early invasion of brain parenchyma, its complete surgical removal is nearly impossible, and even after aggressive combined treatment (association of surgery and chemo- and radio-therapy) five-year survival is only about 10%. Natural products are sources of novel compounds endowed with therapeutic properties in many human diseases, including cancer. Here, we report that the water extract of Ruta graveolens L., commonly known as rue, induces death in different glioblastoma cell lines (U87MG, C6 and U138) widely used to test novel drugs in preclinical studies. Ruta graveolens’ effect was mediated by ERK1/2 and AKT activation, and the inhibition of these pathways, via PD98058 and wortmannin, reverted its antiproliferative activity. Rue extract also affects survival of neural precursor cells (A1) obtained from embryonic mouse CNS. As in the case of glioma cells, rue stimulates the activation of ERK1/2 and AKT in A1 cells, whereas their blockade by pharmacological inhibitors prevents cell death. Interestingly, upon induction of differentiation and cell cycle exit, A1 cells become resistant to rue’s noxious effects but not to those of temozolomide and cisplatin, two alkylating agents widely used in glioblastoma therapy. Finally, rutin, a major component of the Ruta graveolens water extract, failed to cause cell death, suggesting that rutin by itself is not responsible for the observed effects. In conclusion, we report that rue extracts induce glioma cell death, discriminating between proliferating/undifferentiated and non-proliferating/differentiated neurons. Thus, it can be a promising tool to isolate novel drugs and also to discover targets for therapeutic intervention.

Expression pattern of galectin-3 in neural tumor cell lines

Galectin-3 is a member of the galectin family of beta-galactoside-specific animal lectins. Here we show that galectin-3 is constitutively expressed in 15 out of 16 glioma cell lines tested, but not by normal or reactive astrocytes, oligodendrocytes, glial O-2A progenitor cells and the oligodendrocyte precursor cell line Oli-neu. Galectin-3 is also expressed by one oligodendroglioma cell line, but not by primitive neuroectodermal tumor and 4 neuroblastoma cell lines tested so far. In all galectin-3 expressing cell lines, the lectin is predominantly, if not exclusively, localized intracellularly and carries an active carbohydrate recognition domain (shown for C6 rat glioma cells). Moreover, in contrast to primary astrocytes, glioma cells do not or only weakly adhere to substratum-bound galectin-3, probably reflecting an unusual glycosylation pattern. Our findings indicate that the expression of galectin-3 selectively correlates with glial cell transformation in the central nervous system and could thus serve as a marker for glial tumor cell lines and glial tumors.

Plasminogen activator inhibitor-1 in brain tumors: relation to malignancy and necrosis

Tumor necrosis is a common feature of malignant neoplasms. The pathogenesis of tumor necrosis remains poorly documented. Recent evidence has shown a correlation between the presence of tumor necrosis and low content of tissue plasminogen activator in brain tumors and significantly higher levels of plasminogen activator inhibitor-1 (PAI-1) in human glioblastomas. We subjected fresh brain tumor tissue samples (n = 197) to an enzyme-linked immunosorbent assay to determine PAI-1 content. The results were correlated with the presence of edma and necrosis on imaging studies. The samples studied were from normal brain (n = 10), low-grade gliomas (n = 26), meningiomas (n = 47), acoustic neuromas (n = 18), glioblastomas (n = 45), metastases (n = 45), and areas of tumor necrosis (n = 6). The benign tumor samples (n = 96) had 3.5 times less PAI-1 than did the malignant tumors (n = 101). Tumor necrosis samples contained 3.8 times more PAI-1 than did the nonnecrotic malignant tumor samples (P < 0.000001). The benign meningioma samples showed a similar ratio compared with their malignant counterparts (0.35 versus 1.59 ng/mg, respectively, P = 0.0004). Regression analysis results showed a strong correlation between PAI-1 and necrosis (r = 0.47, P < 0.0000028) and, to a lesser extent, brain edema (r = 0.26, P = 0.001). A negative correlation between PAI-1 and tissue plasminogen activator levels almost reached statistical significance (P = 0.07). There was no correlation between PAI-1 content and the tumor size, duration of symptoms, or the sex or age of the patients. The results of this study indicate that malignant transformation is associated with a significant increase in PAlI1 and that PAI-1 may play an integral role in the pathogenesis of tissue necrosis, perhaps via the inhibition of tissue plasminogen activator and the promotion of microthrombosis.

Activities, localizations, and roles of serine proteases and their inhibitors in human brain tumor progression

The plasminogen activation system consists of plasminogen activators and their inhibitors, serine proteases, and serpins. The proteases and inhibitors regulate a variety of processes in tissue morphogenesis, differentiation, cell migration, and cancer cell invasiveness and metastasis. One of the plasminogen activators, urokinase-type plasminogen activator (uPA), binds to a specific surface and provides a localized cell surface proteolytic activity required for the destruction of extracellular matrix, which is a vital step in tumor cell invasion. The proteolytic activity of uPA is modulated by its cell surface receptor, as well as by plasminogen activator inhibitor type-1 (PAI-1) and, to a lesser degree, by other inhibitors. The role of plasminogen activators and their inhibitors in cancer invasion can be demonstrated in the development and progression of malignant brain tumors. Our findings indicate that uPA and PAI-1 expression are dramatically upregulated in malignant brain tumors in parallel with the histological progression of the tumors. The results suggest that these molecules may contribute to tumor invasion in addition to their significant role in angiogenesis. An evaluation of the plasminogen activation system could add diagnostic and prognostic significance to the evaluation of individual patients.

Increased levels of plasminogen activator inhibitor-1 (PAI-1) in human brain tumors

Considerable interest in the roles of serine proteases and serine protease inhibitors (serpins) in regulating physiologic and pathologic tissue remodeling has led to studies that indicate their critical participation in development and diseases of the brain. Plasminogen activator inhibitor-1 (PAI-1) is the most significant regulator of fibrinolysis in plasma, but little is known of the levels or activities of this important serpin in normal brain and brain tumors. For this reason, we estimated qualitative and quantitative levels of PAI-1 in normal human brain and various brain tumors. Western-blot results indicated that a 51 kDa band recognized with polyclonal anti-PAI-1 was more prominently in metastatic and glioblastoma than in meningiomas and low-grade gliomas; normal human brain lacked any detectable band. Reverse zymography also showed high levels of PAI-1 in malignant brain tumors. The complex formation with 125I-urokinase demonstrated that PAI-1 complex levels were increased in metastatic and glioblastoma when compared with low-grade gliomas and meningiomas. Since PAI-1 acts as a modulator of fibrinolysis, a better understanding of the balance between serine proteases and PAI-1 is likely to enhance our knowledge of brain tumor biology.

Expression of plasminogen activator and plasminogen activator inhibitor by rat mesothelioma induced by asbestos

We have investigated the expression of plasminogen activators (PAs) and PA inhibitors (PAIs) by an asbestos-induced mesothelioma. Using zymographic, immunological and biochemical techniques it was demonstrated that cell lines derived from the tumor express high levels of PAI and low levels of a UK-like PA. Adherent and partially non-adherent variants of the mesothelioma expressed indistinguishable amounts of PAI and UK. Based on partial biochemical characterization, the PAI secreted by the mesothelioma cells was a set of PAIs which consisted of PAI-1 in addition to other species. These observations indicate that the difference in growth phenotype of the adherent and partially non-adherent lines was not due to detectable differences in PA and PAI expression.

Human HuH-7 hepatoma cells express urokinase and plasminogen activator inhibitor-1: identification, characterization and regulation by inflammatory mediators

The human hepatoma HuH-7 cell line was shown to constitutively express both a plasminogen activator (PA) and a plasminogen activator inhibitor (PAI). Four sublines of the HuH-7 cell line were analyzed and found to express differing amounts of both PA and PAI. The plasminogen activator produced by these cells was identified as urokinase based upon molecular weight, inhibition of activity with anti-UK but not anti-t-PA antibodies, adherence to an anti-UK affinity column and by Northern blotting demonstrating positive hybridization with the cDNA for UK, but not with the t-PA cDNA. The inhibitor produced by HuH-7 cells was identified as PAI-1 by molecular weight, immunoblotting techniques, adherence to an anti-PAI-1 affinity column, and by Northern blotting demonstrating positive hybridization with the cDNA for PAI-1, but not with the PAI-2 cDNA. The expression of both UK and PAI-1 by HuH-7 cells could be modulated by cytokines known to influence the acute phase response. The addition of interleukin-1 (IL-1) induced the expression of both UK and PAI-1. The increase of PAI-1 was due to an increase in amount of the PAI-1 mRNA. The presence of both interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF) also increased UK and PAI-1 levels, although not as dramatically as IL-1. The addition of IL-1 together with IL-6 produced a slight synergistic response with respect to PAI-1 expression. This suggests that PAI-1 is able to respond to mediators which aid in the induction of the acute phase response. These studies demonstrate that cells of liver origin are able to produce components of the fibrinolytic system. The synthesis of these components can be altered by inflammatory mediators and thus may be involved in hepatic regulation of fibrinolysis in both normal and diseased states.

Modulation of plasminogen activator and plasminogen activator inhibitor expression in the human U373 glioblastoma/astrocytoma cell line by inflammatory mediators

The human U373 glioblastoma/astrocytoma cell line was found to constitutively produce and secrete a plasminogen activator and a plasminogen activator inhibitor. The plasminogen activator was identified as urokinase based on apparent molecular weight, immunoblotting with anti-urokinase antibodies, and Northern blotting with a human urokinase cDNA probe. The inhibitor secreted by U373 cells was found to be related to the PAI-1 molecule based on reactivity with anti-human PAI-1 antibodies, apparent molecular weight, and Northern blot analysis with a human PAI-1 cDNA probe. The expression of both urokinase and the PAI-1-like molecule by U373 cells could be modulated by phorbol myristate acetate or by inflammatory mediators such as interferon-gamma and interleukin-1. In the case of interleukin-1, the alpha form exhibited no detectable effect while the beta form not only elevated inhibitor levels, it also appeared to induce the production of tissue plasminogen activator. Thus, in these cells interleukin-1 beta induces alterations in PA and PAI expression and interleukin-1 alpha does not, even though the two forms are reported to utilize the same cellular receptor.

Biological significance of tissue plasminogen activator content in brain tumors

Fresh brain-tumor samples were obtained at operation and analyzed for their content of tissue type plasminogen activator (tPA) using an activity assay (gel chromatography zymogram) and an enzyme-linked immunospecific assay. The specimens were taken from 23 glioblastomas, 35 metastatic tumors, 42 meningiomas, 16 low-grade gliomas, and seven acoustic neurinomas; seven specimens were from normal brain. A strong correlation was found between the results of the two assays (r = 0.77, p less than 0.0001). There was a threefold difference in the tPA content of the benign tumors as compared to malignant tumors (p = 0.0006), the latter having less tPA. Histologically benign meningiomas contained higher tPA than malignant meningiomas (p = 0.01); however, the difference between low-grade gliomas and high-grade gliomas was less evident. Overall regression analysis data have shown an inverse relationship between the tissue content in tPA and the presence and degree of tumor necrosis and peritumoral brain edema (p = 0.004 and p = 0.0004, respectively). This finding was most consistent in the glioblastoma group where the correlation coefficient values were r = 0.53 and r = -0.55, respectively. There was no significant correlation between the tissue tPA content and the age and sex, steroid use, or plasma tPA of the patients or the duration of symptoms. In summary, this is the first demonstration of tPA in a large series of human brain tumors and in normal brain. The differences observed have clear biological significance and, although the source of tPA in tumor tissue is still unknown, a relative reduction in tPA in tumor tissue may play an integral role in the development of tissue necrosis and tissue edema. The lack of tPA in tumor necrosis was not due to tissue destruction and cell death since urokinase was readily detectable in that tissue.

Inhibitors of urokinase and thrombin in cultured neural cells

Recent studies have suggested important roles for certain proteases and protease inhibitors in the growth and development of the CNS. In the present studies, inhibitors of urokinase or thrombin in cultured neural cells and serum-free medium from the cells were identified by screening for components that formed sodium dodecyl sulfate-stable complexes with 125I-urokinase or 125I-thrombin. Rinsed glioblastoma possessed two components that complexed 125I-urokinase. One was type 1 plasminogen activator inhibitor (PAI-1), because the 125I-urokinase-containing complexes were immunoprecipitated with anti-PAI-1 antibodies. The other component formed complexes with 125I-urokinase that were not recognized by antibodies to PAI-1 or protease nexin-1 (PN-1). Its identity is unknown. In addition to these cell-bound components, the glioblastoma cells also secreted two inhibitors that formed complexes with 125I-urokinase; one was PAI-1, and the other was PN-1. The secreted PN-1 also formed complexes with 125I-thrombin. It was the only thrombin inhibitor detected in these studies. Human neuroblastoma cells did not contain components that formed detectable complexes with either 125I-urokinase or 125I-thrombin. However, human neuroblastoma cells did contain very low levels of PN-1 mRNA and PN-1 protein. Added PN-1 bound to the surface of both glioblastoma and neuroblastoma cells. This interaction accelerated the inhibition of thrombin by PN-1 and blocked the ability of PN-1 to form complexes with 125I-urokinase. Thus, cell-bound PN-1 was a specific thrombin inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)